Mercury vapor generating means for discharge tubes



Sept. 10, 1968 R. RIGOT 3,401,295

MERCURY VAPOR GENERATING MEANS FOR DISCHARGE TUBES Filed April 19, 1965 200 M 30. 60C! 890 1000C T INVENTOR Z R-R/GOT AT'YURNEY United States Patent Office 3,401,296 Patented Sept. 10, 1968 3,401,296 MERCURY VAPOR GENERATING MEANS FOR DISCHARGE TUBES Roger Rigot, Paris, France, assignor to CSF-Compagnie Generale de Telegraphic Sans Fil, Paris, France Filed Apr. 19, 1965, Ser. No. 449,004 Claims priority, appligation France, Apr. 29, 1964,

14 Claims. 61. 313-174 ABSTRACT OF THE DISCLOSURE The present invention relates to discharge tubes having an enclosure containing mercury vapor either in relatively large quantity for operational purposes, or in the state of traces for stimulating some predetermined properties. It is known in the prior art to introduce mercury vapor into these tubes by providing within the evacuated enclosure an auxiliary vessel containing some amount of mercury from which vapor is released under the action of heat, thereby generating the mercury vapor medium which is required for normal operation of the tube.

Unfortunately, the metallic mercury used in the prior art release its vapor also during the manufacturing step of removal of gas from the tube, i.e., during the period when the tube exposed to heat still remains connected to the pumping means. Some quantity of mercury vapor is then evacuated by the pumping means, causing a substantial loss of mercury vapor before the tube is delivered for normal operation. Therefore, at the beginning of normal service of the tube, the mercury vapor atmosphere within the closed or sealed enclosure becomes poor, so that the lifetime of the tube is reduced.

Accordingly, it is an object of the present invention to overcome the drawbacks and shortcomings of prior art methods of producing mercury vapor within an evacuated enclosure.

Another object of the invention is to provide a mercury vapor tube having a relatively long lifetime.

A further object of the invention is the provision of a mercury vapor tube wherein the mercury vapor medium is generated only after the termination of the manufacturing step of removing the gas, when the evacuated enclosure is already disconnected from the pumping means and is closed.

A still further object of the invention is the provision of a mercury vapor tube in which gases are removed by applying temperatures up to about 600 C., substantially without any mercury vapor generation during this treat ment.

These and other objects, features and advantages of the present invention will become more obvious from the following description, when taken in connection with the accompanying drawing, wherein:

FIGURE 1 shows a characteristic of loss of Weight in dependence of temperature for the substance used for generating mercury vapor according to the present invention, and

FIGURE 2 shows diagrammatically a mercury vapor tube using the improvement according to the present invention.

The present invention essentially consists in the use, for generating or producing mercury vapor within closed or sealed enclosures of tubes requiring such an environment, of a substance containing at least in part a chemical product known as mercury pyrophosphate and having the chemical formula Hg P O When a curve is plotted showing along ordinates the loss of weight G (in percent) of mercury pyrophosphate in vacuum in dependence on temperature T (in C.) along abscissae, then a curve shown in FIGURE 1 is obtained. It is seen therefrom that mercury pyrophosphate has the feature of substantially not releasing mercury vapor below about 600 C., further of beginning to release more and more mercury vapor between about 600 and 800 C., and finally of becoming exhausted near 800 C., and the loss of weight at this temperature attaining 70%, a proportion corresponding to theoretical content of Hg in Hgzpgoq.

It results therefrom that mercury pyrophosphate can be successfully applied to the tubes in which the step of gas removal is effected at temperatures lower than about 600 C.

FIGURE 2 shows as an example only a diagrammatic view of a tube including within an evacuated enclosure 1 a system of electrodes 2 supported by the rods 3. For instance, to one of the rods 3 is attached an auxiliary vessel 4 composed of two shells connected together by a plurality of welding points and containing several milligrams of a substance composed at least in part of mercury pyrophosphate. Prior to closing or sealing of the enclosure 1, the tube was connected to pumping means (not shown) and subjected to action of heat at a temperature lower than about 600 C. During this period, there was substantially no release of mercury vapor from the pyrophosphate. After the tube is disconnected from the pumping means and the enclosure 1 is closed, the vessel 4 is exposed to a heating action at a temperature between about 600 and 800 C., by means of any known method, such as for instance, high frequency. The mercury vapor is then released from the pyrophosphate and passes through the nontight junction between the edges of two shells composing the vessel 4, to fill the enclosure 1, so that the tube is ready for normal operation. The release of vapor should also be controlled by acting on the source of heat.

The mercury pyrophosphate for this use should be preferably very pure, with a proportion of impurities not in excess of several parts per million, and rigorously dry at the instant of its introduction into the vessel4.

If during the treatment or operation of the tube a temperature of the order of 750 C. is never exceeded, the mercury pyrophosphate can be used without mixture with any other substance. If, however, such a limit is exceeded during the operation or during a manufacturing treatment, or if the tube is subjected to the danger of such excess temperatures during its treatment, even if only for a short duration, then there is a risk that not only mercury but also oxygen is released from the pyrophosphate, this being harmful for certain electrodes of the tube.

To obviate this risk, the mercury pyrophosphate will be used in such a case in mixture with an oxygen reducing substance, for instance, a powder of metal such as aluminum, aluminum-j-magnesium, titanium, zirconium, columbium and the like, the proportion being thereof chosen for instance between 25% and by weight of the total mass of the mixture.

This composition enables mercury pyrophosphate to be dissociated at temperatures above 750 C., without any trace of oxygen accompanying the release of mercury.

While I have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art. Thus, the invention is applicable to all kinds of mercury vapor tubes, such as thyratrons, luminescent tubes, display tubes, certain tubes for medical use, etc. Therefore, I do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A method for producing a mercury vapor environment within an evacuated closed enclosure, particularly discharge devices, comprising the steps of locating within said enclosure a substance consisting at least in part of mercury pyrophosphate, applying heat at a first temperature to said substance, and subsequently applying heat to said substance at a second temperature higher than said first temperature.

2. A method as claimed in claim 1, wherein said heat is applied at said first and second temperatures between about 600 and 800 C.

3. A method as claimed in claim 1, wherein said substance consists of a mixture of mercury pyrophosphate with an oxygen reducing substance.

4. A method as claimed in claim 3, wherein said reducing substance is a metal.

5. A method as claimed in claim 4, wherein said metal is in powdered form.

6. A method as claimed in claim 4, wherein said metal is selected from the group essentially consisting of aluminum, magnesium, titanium, zirconium, columbium, and mixtures thereof.

7. A method as claimed in claim 3, wherein said reducing substance forms a proportion between about 25 and 75% by weight of the total mass of said mixture.

8. In a mercury-vapor filled discharge tube, means for producing a mercury vapor environment comprising within an evacuated enclosure of the discharge tube a substance consisting at least in part of mercury pyrophosphate.

9. In a mercury-vapor filled discharge tube, means-for producing a mercury vapor environment comprising within an evacuated enclosure of the discharge tube an auxiliary vessel intercommunicating with the interior of said enclosure, and a substance consisting at least in part of mercury pyrophosphate, located within said vessel.

10. A tube as claimed in claim 9, wherein said enclosure contains a system of electrodes, and wherein said vessel is attached to said system of electrodes.

11. A tube as claimed in claim 8, wherein said substance consists of a mixture of mercury pyrophosphate with an oxygen reducing substance.

12. A tube as claimed in claim 11, wherein said reducing substance is a metal.

13. A tube as claimed in claim 12, wherein said metal is in powdered form. t

14. A tube as claimed in claim 12, wherein said metal is selected from the group essentially consisting of aluminum, magnesium, titanium, zirconium, columbium, and mixtures thereof.

References Cited UNITED STATES PATENTS DAVID J. GALVIN, Primary Examiner. 

